The present invention generally relates to increasing data throughput and quality in a wireless communication system and, more particularly, to systems and methods involving selection of air interface transmission modes based on access network capacity in radiocommunication systems.
The growth of commercial communication systems and, in particular, the explosive growth of cellular radiotelephone systems have compelled system designers to search for ways to increase system capacity without reducing communication quality beyond consumer tolerance thresholds. At the same time usage of mobile communication equipment for transmission of data rather than speech has become increasingly popular by consumers. The ability to send and receive electronic mail and to use a web browser to obtain world-wide-web access is frequently discussed among services that will be used more and more in wireless communication systems. In response to this, communication system designers search for ways to efficiently transfer data information to and from mobile users and, in particular, to provide high data rate transfer capability.
In considering various technologies for next generation, high data rate radiocommunication systems, both time division multiple access (TDMA) and code division multiple access (CDMA) technologies are potential candidates in various parts of the world. In TDMA, radio channels are created by dividing frequencies into a number of time slots and associating a given number of time slots with each channel. Capacity can be increased, e.g., to provide higher data rates, by increasing the number of time slots associated thereiwith.
In a typical CDMA system, an information data stream to be transmitted is impressed upon a much higher bit rate data stream produced by a pseudorandom code generator. The information signal and the pseudorandom signal are typically combined by multiplication in a process sometimes called coding or spreading the information signal. Each information signal is allocated a unique spreading code. A plurality of coded information signals are transmitted as modulations of radio frequency carrier waves and are jointly received as a composite signal at a receiver. Each of the coded signals overlap all of the other coded signals, as well as noise-related signals, in both frequency and time. By correlating the composite signal with one of the unique spreading codes, the corresponding information signal can be isolated and decoded.
In addition to selecting an access methodology, next generation systems must also consider suitable techniques for increasing the information rates associated with conventional implementations of those techniques. For example, higher level modulations and allocation of additional timeslots per channel are being considered to increase the throughput over the air interface, i.e., the interface between mobile stations and base stations. However, in order to completely accommodate an increase in information transmission rates, the entire system, not just the air interface, must be enhanced or modified to support the desired, higher throughput rate.
For example, in the pan-European standard known as the Global System for Mobile (GSM) communications, there exists an interface between the base transceiver system (BTS) and the base station controller (BSC), which interface is commonly as referred to as the A-bis interface. The A-bis interface is specified in GSM Technical Specifications (BSC-BTS) interface, GSM 08.5 Series, the description of which is incorporated here by reference. This interface is designed to provide for a throughput (per air interface connection) of up to about 16 kbps. However, system designers now envision much higher information rates being accommodated over the air interface, i.e., on the order of 64 kbps. Accordingly, the throughput associated with this network interface, as well as other interfaces within GSM systems and those in other systems, needs to be addressed in light of the anticipated increases in capacity over the air interface.
An example of how the GSM system could be extended to provide for increased capacity is illustrated in FIG. 1. Therein, a number of different types of packet data GPRS/EGPRS services are described in terms of channel coding (i.e., convolutional coding) rate, air interface data rate and the number of terrestrial bandwidth (BW) units need to handle the corresponding air interface data rate. One relatively straight forward solution for accommodating such a change to the air interface capacity is to simply increase the throughput/capacity of the access network to match that provided for the air interface. For example, to accommodate the changes to GSM proposed in FIG. 1, the A-bis interface could be extended to provide eight PCM slots (i.e., 512 Kbps) per transmitter unit to handle the maximum throughput defined in FIG. 1 of about 64 kpbs.
However, costs associated with extending the capacity of the access network are severe. Additionally, several operators lease capacity in access networks from access network providers, e.g., other operators, and they are interested in limiting the leasing costs by an efficient usage of access network resources. Thus, it would be desirable to provide techniques and systems which are able to avoid reaching the capacity limits of the access network as a possible alternative to extending the capacity thereof.
Moreover, Applicants anticipate that, in some implementations, designers and/or network operators may opt to increase the throughput of the air interface to a point which reaches or exceeds the capacity of the access network. Accordingly, it would also be desirable to find techniques for controlling allocation of call blocking and/or packet delay which will result when the access network reaches or exceeds its capacity limits.
These and other drawbacks and limitations of conventional methods and systems for communicating information are overcome according to the present invention, wherein Applicants present techniques and systems for air interface transmission mode selection, eg., selection of transmission parameters affecting the information rate such as modulation type and/or forward error correction coding type, based, least in part, on a current load experienced in the access network. For example, when a new call is being set-up, the load on the access network can be checked. If the load has reached a predetermined threshold, e.g., close to or equal to the access network capacity, then the system can free resources by reducing the information rate associated with ongoing calls. Alternatively, the system may elect to reduce the information rate permitted for the new call so that it fits within the available access network resources.
According to another exemplary embodiment, a plurality of call service classes are defined. Certain call service classes, which are less delay tolerant, can be reserved sufficient resources on the access network interface so that these connections are serviced without blocking or delay on the access network regardless of how highly loaded the air interface becomes. Other service classes, which are more delay tolerant, are reserved less resources on the access network and may experience greater delay and/or more blocking if the air interface becomes more heavily loaded. The invention is also readily applicable to access networks wherein Asynchronous Transfer Mode (ATM) techniques are utilized, ATM can be used to increase access network utilization by statistical multiplexing of different data streams.
Other system processes, e.g., cell selection and handoff, can also be performed in light of access network loading.